Ionized air stall detector



y 15, 1952 P. J. CAMPBELL 2,603,695

IONIZED AIR STALL DETECTOR Original Filed April 11, 1944 F/G. a

4Z4 /Z H 7 Il/GH VOLTAGE Q GENERATOR DETECTOIR AM'IIII 6% a2 L 3 AMPflfi/ER /Zfl" x Z k Q INVENTOR .PAUL J CAMPBELL A 7' TORNEY This application is a Patented July 15, 1952 l 3w Q aul JZCampbell, Middletown, Conn a's signor to' I "United sAi'rcraft Corporation, East Hartford,=-

-' Conn.,-a-corporationof Delaware w I gan application April fill, 1944, *ser iaifixio. 530,483. Divided and thisj application April 3,

1e51, Serial N .'2 19,072

ivision. of application Serial No. 530,483; filed: April 11, 1944, which matured into Patent No.=;2,569,974, issued October This invention relates to the measurement of a flow characteristic ofa free airstream.

Anpbject of this invention. is ,toprovide an improved method and apparatus for measuring aflow' characteristic; such asdirection of flow of ..an:- airstream,=and;. particularly of a free or unconflnedairstream." 11:

Afurtherobject' of. this invention is to contribute to the aircraftinstrumentart an-instrument based on anew principle, utilizingionized air reference regions, for indicating the nature of the airflow. over an airfoil, and specifically for indicating the approach or presence of a stalling condition. I I

.. Other objects-and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate what is now considered to be a preferred embodiment of the invention. i

: Figs. -1 and 2 are schematic cross-sectional views of an airfoil having an ionizing device and a pickup or detector device thereon for indicating the approach of presence of a stalled condition by determining the nature of the airflow over the airfoil at varying angles of attack.

Figs. 3 and 3a. are similar to Figs. 1 and 2 but show modifications of the pickup device.

Fig. 4 is a diagrammatic view of a wind tunnel installation, showing how the sending device, or spark gap, and the receiving device, or detector. of this invention may be utilized to determine the airflow characteristics of an airfoil.

According to this invention a section or portion of the fluid in a flowing fluidstream is ionized teams (01. 171-311).

certain point, the airfoil'stalls, or the' airflow Aabreaks away fromthe. upper surface of the wing as shown in-Fig; 2, the airflow over the rear o'r aft portion of thewingbecoming-turbulent as shown at B in Fig. 2. If the ionizing device l2 and the detector orpickup Hl' are positioned as shownin Fig. 1, the ionized segments'will'ttravel from .the'sender l2- ov'er the upper surface of the wing closely adjacent thereto and-will be received by the pickup I4. But if 'the airfoil is stalled; the airflow will-be pulled away or will be violently displaced relative to the rearward portions ofthe upper surface of the airfoil and .the ionized segments will not contact the pickup l4, or else 'willbe so dissipated throughout the airstream as to be incapable of actuating .oroperating'the receivingapparatus." By properly positioning pickup l4 along the upper surface of the airfoil, chordwise'thereof', failure of the pickup to produce impulses while the sending device I! is functioning will indicate the presence of a stalled condition of the airfoil, or preferably'theapproachof-a' stalled condition, depending upon the location of the pickup: 1 "Fbr stall indicating purposes the ionized air stream need not be in; longitudinal segments but can be made continuous or uninterrupted in a longitudinal direction. The sender may be continuously energized to constantly ionize a crosssectional portion of the airstream passing over the upper surface of the airfoil. Under these conditions the pickup will be constantly energized by the charged air as long as the airfoil is within the normal range of angles of attack. When the airfoil exceeds this normal range and approaches the stalled condition, the airflow will begin to pull away or, be turbulent at the rear portion of the airfoil, displacing the ionized air with respect to to render it electrically distinguishable from the remainder of the fluid in the fluidstream, yet the physical properties of said section or portion are not materially afl'ected. Thus, the flow characteristics of the fluidstream are not materially altered and yet may be measured directly, by electrically sensing the passage or location of the electrically distinguishable fluid portion or ionized fluid region with respect to a point or points which are fixed relative to the fluidstream.

The ionizing and detecting devices of this invention may be used to indicate the presence of a stalled condition or the approach to a stalled condition of an airfoil. Airflow around an airfoil at normal angles of attack is substantially laminar or streamlined as shown at A in Fig. 1. When the angle of attack of the airfoil is varied beyond a' the pickup device, resulting in a failure of its indication or interruption of its operation, which may be utilized in a manner obvious to those skilled in the art to actuate a warning device to inform the pilot that the aircraft is in a dangerous attitude or at a dangerously low speed.

The arrangement of Figs. 1 and 2, which utilizes the coaxial or concentricelectrode pickups,

will also indicate a lateral movement of the *ductors I20, I22. Thus as illustrated in Fig. 3a?- v to operate ,a warning signal.

, may be simp lyr a galvanometer,--or a combined amplifier and microammeter for, indicating changes in impedance of the air gap between conthe conductors I2|Ja., I22 a, may be connected to; i a D. Cbamplifier which in turn passes a signal to' a meter and/or light. Conductors I:26, I;22;pref-?,

wing Iflflfand are elongated spanwise thereofz- Thus, the charged airstream created by thesend-' er I 2 (which may be formed either as a continue; f 0115 ionized stream in'the direction of the air'- flow orin'the' form of segments) will contact the electrodes I20, I22 and actuate the detector126 when the airfoil is within a safe range of angles of attack relative to the airstream, regardless of whether-or not the airfoil isskidding orslipping relative 'to'theairstream. J'Because e1ectrodesI20;

I I22 are elongated 1atera'l1y,:the idetector, will still be actuated even though thereis some movement 25 of the'tcharged airstream spanwise oflthe airfoil,'after*it"leaves'the sender; I2. But whensthe airfoil approachesthe; stalled condition, ;-:the charged Iairstream will be :zdefiected upwardly with i respect to] the airfoil; away from thecon '30 ductors 420,.- I22 I and "the I resulting cessation of the'current fiowto'the detector may be utilized Y 'Theflow direction principle applied toFigs.-1,2 A and 3-and-:3c:as a stall, slip-,ior skid indicating device may also be utilized for other purposesyas shown. in Fig. 4. 'Here thewind tunnel I50j' pro vides an airflow over airfoil I 52. The sender I2 and pickup TI4 are mounted on movable supports I 54, I56,'res'pectively, so that the direction of the airflow maybe determined. relative to the airfoil I52 by creating ionized aireportions at a-selected position' within the airstream, theqdirection of 7 flow being indicated by moving pickup I-4yuntil an indication is noted, on a galvano meter or other '45 electrical'indicating device.-.,

It is to be understood that the invention is not limited to the specific embodiments herein illustrated and described, but may be used in other ways without departure from the spirit of this.

novel concept; claima 1;;In a' "Stan" idem-staffer is ,aiferarc airfoil,

a device for creating an ionized streak of air in the airstream passing over the upper surface of 0. saidjairfoil,,apickup device for sensing the posi- "tion'of the path of said ionized streak of air rela- ,tive tosaid airfoil, and an indicator operatively erably lieclose to'or in the upper-contourofthe connectedto :said'pick-up device for indicating 1 the presence of; said ionized streak.

,2, A stall detector for aircraft airfoils comprisingin eans for ionizing a portion of the airstream passingrcversaid airfoil, means located on said airfoil downstream of said ionizing means at a position where the airflow is turbulent in the stalled condition and. laminar in the non-stalled position for sensing the presence'or'absenceat said position of said ionizedair portion, and'indi cating means operatively' connected to saidxsensing means for indicating the presence or absence of saidportion.

3. In a stall indicator-for an aircrafthaving a lifting surface, mean locatedon said surface for ionizing a portion of the airstream passing over said surface-means. located downstream of said ionizing means for sensing the: presence or abe sence of said portion relative togafpredetermined point spaced from said "surface including spaced electrical'pickupa'and indicating means opera tively connected to'said pickups. 1 "PAUL-'QI ECAMPJQELLJ REFERENCES CITED I The following references are of recordin the file ofthis'patentt' uNi'rED's'rA Es P T NT S.f Number Name 'Date r 1,808,709" i'B1ak e' L. June 2,1931 

